You're absolutely correct; a lot of places would be totally uninhabitable if the ocean currents shifted even just a tiny bit. My own country, Norway, would most likely not be habitable if it was not for the North Atlantic Current. Some scientists are also afraid that this current might shift or change, so it's not an unrealistic fear you have.

Extreme weather is one of the biggest problems of climate change, and there are many places where you can already feel and measure the difference. And it will most likely only be more extreme as time goes by. But as you said, we might be able to stop it! The problems with the ozone layer is almost fixed now, and that seemed almost just as hopeless at the time.